1. Field of the Invention
The present invention relates to systems and processes used in manufacturing integrated device die, such as integrated circuits and laser diodes, including diode lasers formed on conductive substrates. More particularly, the present invention provides for securing wafers having conductive substrates, during the process of cutting the wafers into individual die, and further provides for securing the die separated from the wafers during and after the wafer cutting process.
2. Description of Related Art
Sapphire Al2O3 is used as a substrate for the growth of Gallium Nitride GaN in commercial laser diode manufacturing systems, and can also act as the substrate of the finished product. However, the use of sapphire substrates introduces certain problems.
For instance, sapphire is an electrical insulator and this causes problems when it is used as a wafer substrate in the fabrication of laser diodes. Because it is an insulator, electrical contacts to the diodes are usually placed on the wafer's active surface, and these contacts occupy areas that would otherwise be utilized for generation and emission of light.
Efforts have been made to implement laser diodes using GaN with other substrates. These approaches typically involve removal of the GaN from the sapphire substrate on which it is grown, and then remounting it on another substrate. Advantages of this approach arise because copper or other metal substrates are excellent heat and electric conduction materials. A light emitting diode or laser diode LED with a metal substrate can be driven with higher current and yield brighter output. In addition, the device with good electric conduction to the substrate requires only one wire bonding on the active surface, and yields higher output. Furthermore, the sapphire substrate used for growth of the GaN may be reused for reduced cost.
For example, U.S. Pat. No. 6,365,429 teaches a method by which “removal of the sapphire substrate after growth of the laser diode array structures simplifies providing electrical contacts to the laser diode arrays and avoids special architectures while allowing a superior heat sink to be attached to the laser diode arrays. The laser diode array may be attached to a thermally conductive wafer before or after substrate removal by soldering, thermo-compression bonding or other means.” (col. 2 11. 20–28)
However, no known method or tools to dice this type of wafer have been applied on a commercial scale.
Present methods of separating a wafer based on a sapphire or crystalline semiconductor substrate into die involve scribing the wafer after first adhering the wafer to a flexible sheet, known as “blue tape”. After scribing, mechanical pressure is applied to break the wafer along the scribe lines, leaving the die attached to the flexible sheet for their subsequent removal.
However, wafers having metal substrates cannot be separated into die using scribing techniques. Rather, wafers having a metallic substrate, for example one made of copper, must be cut completely through to obtain separated die. Cutting completely through the wafer would damage an adhesive sheet attached to the wafer, unless very precise control of the cutting process were possible. Furthermore, if an adhesive sheet is not attached to the wafer prior to cutting the die, in order to avoid the damage, the separated die would be difficult to handle during and after the cutting of the wafer. Thus, there is a need for a method and system for securing both the wafer and the separated die during and after the cutting of the wafer.
It is desirable, therefore, to provide a system and method for dicing wafers having conductive or metallic substrates, for use in fabricating die in large volume, in an efficient manner that maximizes the die-manufacturing yield. Furthermore, it is desirable that such a system be compact, safe to operate, and low cost.